Light absorption effect in a Ton-scale liquid argon detector

A liquid argon detector, consisting of 2.2 metric tons of liquid argon, is used to observe a significant alteration in the scintillation light yield of liquid argon while maintaining a high value for the slow decay time. The absorption effect due to trace impurities on 128 nm photons during vacuum-UV light transmission can account for this phenomenon. This explanation is substantiated by a combined analysis of data pertaining to variations in light yield and slow decay time with impurity concentration. The relationship between the light absorption length in liquid argon and detector light yield is assessed by employing GEANT4 detector simulations. The measured light yields suggest a reasonable range for the light absorption length, approximately 3-5 m or 8-10 m, as observed in two purification experiments. To enable future large-scale liquid argon detectors to achieve comparable light yields, it is imperative to significantly enhance the light absorption length of liquid argon.